Day of the Lord

The sun will be turned to darkness and the moon to blood before the coming of the great and dreadful day of the Lord. And everyone who calls on the name of the Lord will be saved; for on Mount Zion and in Jerusalem there will be deliverance, as the Lord has said, among the survivors whom the Lord calls. - Joel 2:31-32

the time when Jesus comes back to earth, it is said that it's going to be both "great and dreadful". it will be joyful for the faithful and righteous, but terrible for the wicked. God said that there will be everlasting joy and redemption, but only after the terrible wrath of God's judgments have been unleashed. the God-breathed scripture tells us to warn each other and prepare for it. in fact, half of the book of Joel warns us to let go of our earthly obsessions, and come repent and cry out to God. we must keep our faith because Satan is going to do everything in his power to stop us from rejoining our heavenly Father.